Paper 2017/573

Ouroboros Praos: An adaptively-secure, semi-synchronous proof-of-stake protocol

Bernardo David and Peter Ga{ž}i and Aggelos Kiayias and Alexander Russell

Abstract

We present “Ouroboros Praos”, a new proof-of-stake blockchain protocol that provides, for the first time, a robust distributed ledger that is provably secure in the semi-synchronous adversarial setting, i.e., assuming a delay \Delta in message delivery which is unknown to protocol participants, and fully adaptively secure, i.e., the adversary can choose to corrupt any participant of an ever evolving population of stakeholders at any moment as long the stakeholder distribution maintains an honest majority of stake at any given time. To achieve that, our protocol puts to use forward secure digital signatures and a new type of verifiable random functions that maintains unpredictability under malicious key generation, a property we introduce and instantiate in the random oracle model. Our security proof entails a combinatorial analysis of a class of forkable strings tailored to semi-synchronous blockchains that may be of independent interest in the context of security analysis of blockchain protocols.